00:01
Okay, so in this question, we have a diffraction grating with 3 ,000 lines per centimetre.
00:08
And we have two spectral lines, hydrogen, one of 486 nanometers wavelength and the other of 656.
00:15
We're asked to find a distance between the first order maxima for each of the spectral lines.
00:21
So, in order to do that, we need to use the equation n -lamda equals d -sign theta, where d is the spacing between each line.
00:34
So if there are 3 ,000 lines per centimetre, that means there are 300 ,000 lines per meter.
00:40
You don't necessarily have to convert to meters.
00:45
You can do this in centimetres, but i just think it's safer to always get in the habit and converting to si units.
00:52
So 300 ,000 lines per meter means 1 over 300 ,000 line.
00:57
So 1 over 300 ,000, which is 3 .33 times 10 to the minus 6 meters.
01:06
That is your grating spacing.
01:09
That is d.
01:10
So that will equal the d part of our equation.
01:16
N is the order.
01:18
That's one.
01:19
So we don't need to worry about that for now.
01:21
In fact, we can just full on ignore it.
01:23
So we want to work out, well, these angles here.
01:27
I've actually written them there...